Featured Research

from universities, journals, and other organizations

A dominant hemisphere for handedness and language?

Date:

July 4, 2014

Source:

CNRS

Summary:

Through an innovative approach using a large psychometric and brain imaging database, researchers have demonstrated that the location of language areas in the brain is independent of left- or right-handedness, except for a very small proportion of left-handed individuals whose right hemisphere is dominant for both manual work and language.

Share This

Probability map of the brain regions activated in functional magnetic resonance imaging by a silent sentence production task in a group of 144 right-handed individuals. The color scale indicates the percentage of subjects with significant activation in this area during the task (green: 50%, blue: 65%, red: 80% or more). Note the high asymmetry of the map in favor of the left hemisphere).

Through an innovative approach using a large psychometric and brain imaging database, researchers in the Groupe d'Imagerie Neurofonctionnelle (CNRS/CEA/Université de Bordeaux) have demonstrated that the location of language areas in the brain is independent of left- or right-handedness, except for a very small proportion of left-handed individuals whose right hemisphere is dominant for both manual work and language. This work was published in PLOS One on June 30, 2014.

Related Articles

Humans are the only species in which asymmetric motor behavior is preponderant: 90% of people prefer to use their right hand and 10% their left hand. This motor behavior is "cross-lateralized": when using the right hand, the dominant left hemisphere is activated. Along with motor behavior, language is one of the most lateralized functions of the human body: the networks of brain areas controlling language are located asymmetrically in the brain's left or right hemisphere. Many studies have shown that the left hemisphere is dominant for language in 90% of cases, as it is for motor behavior.

Are the 10% of people who are left-handed and of those whose language is located in the brain's right hemisphere the same? Is the location of language areas in the brain correlated to handedness? To answer these questions, researchers from the Groupe d'Imagerie Neurofonctionnelle recruited a large sample of participants (297) including numerous left-handed subjects (153). Whereas most other studies only relate to right-handers (a majority of the population) these researchers analyzed language lateralization for the first time in a large number of right- and left-handed individuals. The subjects in this sample were assessed using functional MRI while they performed language tests. Three types of language lateralization were then revealed from the images obtained: "typical" with a dominant left hemisphere (present in 88% of right-handers and 78% of left-handers), "ambilateral" without a clearly dominant hemisphere (present in 12% of right-handers and 15% of left-handers), and "strongly atypical" with a dominant right hemisphere (present only in 7% of left-handers). Statistical analysis of this distribution shows that concordance between the dominant hemisphere for handedness and that for language is random, except for a small fraction of the population (less than 1%) for whom the right hemisphere is dominant for both language and handedness.

These results show that knowing an individual's preferred handedness it is not sufficient to determine their dominant hemisphere for language. Researchers will now attempt to elucidate why only a small group of left-handers have a dominant right hemisphere for language, particularly by finding out whether there are genetic variants that might explain this phenomenon. These results also demonstrate that by contrast with a sample including a majority of right-handers, a sample enriched with left-handers composed from a large database shows variability factors in the brain structural and functional correlates: determining the sources of this variability in language lateralization may help to elucidate language pathologies.

Story Source:

The above story is based on materials provided by CNRS. Note: Materials may be edited for content and length.

More From ScienceDaily

More Mind & Brain News

Featured Research

Mar. 3, 2015 — The literary great Marcel Proust wore ear-stoppers because he was unable to filter out irrelevant noise -- and lined his bedroom with cork to attenuate sound. Now new research suggests why the ... full story

Mar. 3, 2015 — Attendance at schools exposed to high levels of traffic-related air pollution is linked to slower cognitive development among 7- to 10-year-old children in Barcelona, according to a new ... full story

Mar. 3, 2015 — No significant change in home habits of smokers have been observed in the aftermath of a ban on smoking in public spaces, researchers report. Greater inspiration to kick the habit likely comes from ... full story

Mar. 3, 2015 — Heart function has been associated with the development of dementia and Alzheimer's disease through a new study. Participants with decreased heart function, measured by cardiac index, were two to ... full story

Mar. 3, 2015 — Children of recently separated or divorced families are likelier to drink sugar-sweetened beverages than children in families where the parents are married, putting them at higher risk for obesity ... full story

Mar. 3, 2015 — Although sedatives are often administered before surgery, a randomized trial finds that among patients undergoing elective surgery under general anesthesia, receiving the sedative lorazepam before ... full story

Mar. 3, 2015 — Why do people shake hands? A new study suggests one of the reasons for this ancient custom may be to check out each other's odors. Even if we are not consciously aware of this, handshaking may ... full story

Mar. 3, 2015 — It appears that stress markers in unemployed people can be found, independent of smoking, alcohol consumption and overweight/obesity. Results from a study suggest that long-term unemployment may be ... full story

Mar. 3, 2015 — On the heels of an American nationwide measles outbreak comes a report that campaigns aimed at scaring people about the consequences of non-vaccination might not be as effective as many think. ... full story

Mar. 3, 2015 — Doctors write millions of prescriptions a year for drugs to calm the behavior of people with Alzheimer’s disease and other types of dementia. But non-drug approaches actually work better, and carry ... full story

Related Stories

July 3, 2014 — Men born in November, December or January are more likely of being left-handed than during the rest of the year. While the genetic bases of handedness are still under debate, scientists obtained ... full story

May 2, 2012 — The way we use our hands may determine how emotions are organized in our brains, according to a recent study. Motivation, the drive to approach or withdraw from physical and social stimuli, is a ... full story

Jan. 31, 2011 — Most people who survive a stroke recover some degree of their motor, sensory and cognitive functions over the following months and years. This recovery is commonly believed to reflect a ... full story

Nov. 5, 2010 — Scientists have identified a genetic variant which influences whether a person with dyslexia is more skilled with either the left or right hand. The finding identifies a novel gene for handedness and ... full story

ScienceDaily features breaking news and videos about the latest discoveries in health, technology, the environment, and more -- from major news services and leading universities, scientific journals, and research organizations.